A digital image or a digital video sequence may be compressed by a compression algorithm in order to satisfy a bandwidth requirement of a transmission medium by which the image or sequence is to be communicated or to satisfy a storage-size limitation associated with a storage medium on which the image or sequence is to be stored. Exemplary, widely used, video-compression methods include MPEG-1, MPEG2, H.264 and other video-compression methods. Many video compression methods are DCT (Discrete Cosine Transform) based and may represent a signal by the sum of smooth, oscillating waves. When bandwidth or storage is insufficient, necessitating high compression ratios, decoded and displayed, or printed, images and videos may exhibit annoying ringing artifacts. Ringing artifacts may be caused by the fundamental inability of DCT-based compression algorithms to accurately represent edges, often making ringing artifacts more visible in the regions of text, diagrams, line drawings and other regions where strong, sharp edges are prominent. In video, some ringing artifacts may not always be visible. Ringing artifacts around stationary or slow-moving objects may be more visually objectionable than those near fast-moving objects. This may be due to the ability of the human visual system to better track objects with slow, or no motion, than objects with fast motion.
Some methods for de-ringing may be designed for use in a decoding loop or may assume knowledge of a decoding process. While such methods may take advantage of information in the codec (coder/decoder), these methods cannot be used in post-processing after decoding. Post-processing after decoding may be necessary because, in practice, ringing artifacts that may not be visible in the output of the codec may become visible after signal processing, for example, enhancement, up-scaling and other signal processing, is applied to the decoded image or video.
Methods and systems for post-processing de-ringing may be desirable.